Bonding is a popular technology that combines multiple individual links or connections into a single aggregated pipe. This process is also referred to as bundling, or inverse multiplexing. FIG. 1 is a block diagram illustrating the concept of bonding. A bonding group 10 has multiple links 12. At the transmit end 14, traffic is distributed to the links 12 based on a link selection method or algorithm. Data traffic is typically in the format of packets, fragments or frames. At the receive end 16, traffic arriving from each of the individual links is collected and reassembled.
Bonding provides two obvious benefits: 1) increasing the overall bandwidth by aggregating multiple links together; and 2) providing redundancy and protection to the overall data transfer, such that when a failed link is removed from the group, or otherwise becomes inoperative, traffic can still pass through other links.
There are many bonding protocols and standards available to date. Some examples include: inverse multiplexing of Asynchronous Transfer Mode (IMA), which is used to carry ATM over multiple time division multiplexed (TDM) links such as E1/T1; multiple link point-to-point protocol (MLPPP), which is used to carry PPP packets over multiple TDM links such as E1/T1; IEEE 802.3ad Link Aggregation (LAG), which describes the bonding of Ethernet connections; and ITU-T G.998.2, which is the bonding protocol for digital subscriber line (DSL) lines.
Existing bonding protocols have three common characteristics. The first common characteristic is that they only consider the same type of links in a bonding group, i.e. the links in the group are homogeneous. One example of this homogeneity is being of the same link type, meaning that the links are comprised of the same physical medium and thus have the same data transfer characteristic. For example, IMA and MLPPP deal with TDM (e.g. E1/T1) links only. LAG is for Ethernet (Gigabit Ethernet or Fast Ethernet) links only. G.998.2 only works on ADSL or VDSL links.
Because the links are of the same type, it both implies and assumes that all links are equal in terms of quality, reliability and priority. The only difference among links is the speed. IMA and MLPPP protocols allow the links to have different speed. Consequently, when data (e.g. a packet) arrives at the transmit end of the bonding group, the decision of which link should be selected to transport this data is relatively simple. Since all the links in the bonding group are of the same quality, a protocol that simply selects the next available link is sufficient to ensure the benefits of bonding are applied to the data transfer. The simplest examples of this are known as Round Robin (RR) link selection and Weighted Round Robin (WRR) link selection.
The second common characteristic of existing bonding protocols is, because of the first characteristic, the link selection algorithms are typically implemented as either round robin or weighted round robin. The RR algorithm always selects the next link in the group, and cycles through the links one by one. The WRR algorithm cycles through the links in the same fashion as RR; however, once a link is selected, it will transmit more than one packet or fragment. The amount of data allowed is proportional to the weight. In weighted round robin, each link has a weight attribute (representing the link speed) that is considered in link selection.
The third common characteristic of existing bonding protocols is that link speed is considered as static. The link speed does not change once a link is added to the group.
The above characteristics of known approaches become a serious limitation for newer applications, unable to meet the requirements of mobile backhaul or other transport applications. FIG. 2 illustrates an example of bonding in mobile backhaul.
Mobile backhaul is a way to transport base-station traffic from a cell site 20 to a central office 22. E1/T1 links 24 are widely used for 2G/3G backhaul. With the fast growing of data rate, E1/T1 bandwidth becomes insufficient. Carriers are adding Ethernet links 26 (copper or fiber) to the cell site, or a microwave link 28 in case cabling is prohibited, in addition to the already existing TDM links. The result is that different types of physical medium (E1/T1, DSL, active Ethernet, microwave etc.) may co-exist at the cell site.
Telecommunications are starting to bond links of different types together, such as in the example of mobile backhaul in FIG. 2. For example a copper link, which is a very reliable medium for data transfer, may be put in the same bonding group as an RF link, which is a much less reliable medium for data transfer. To ensure that the overall data transfer is protected, the method used to select the next link cannot just be a random selection of the next available link, as is the case in existing bonding protocols.
It is desirable to provide link selection in a bonding protocol that addresses at least one of the shortcomings of existing approaches.